1. Field of the Invention
This invention relates to torque-applying apparatus and in particular to such apparatus responding to a yielded condition of the threaded members to effect a discontinuation of the threading operation.
2. Description of the Prior Art
In U.S. Pat. No. 3,827,506 of Sydney Himmelstein et al, which patent is owned by the assignee hereof, an improved torque-applying apparatus is disclosed having one or more torque motors arranged for forcibly threading one or more pairs of first threaded members into tightened association with corresponding second threaded members. The control of the apparatus causes firstly a seating of the first threaded members relative to the second threaded members by a low torque, high speed threading operation. When the seated condition of all of the threaded members is sensed, the control effects a low speed, high torque further threading of the seated threaded members until a preselected maximum torque condition is achieved corresponding to the desired tightened set condition of the threaded members.
In U.S. Pat. No. 3,643,501, of Reginald W. Pauley, a wrenching system and method is disclosed wherein the torque on the fastener applied by the wrench is measured concurrently with the measurement of the angle through which the fastener is rotated. The torque and rotation angle are simultaneously compared and when the rotation angle begins increasing at a nonlinear rate relative to the increase of torque, a signal is created indicating that the strain on the fastener exceeds the elastic limit thereof. The signal may be utilized to actuate a shutoff means to stop the wrench.
In U.S. Pat. No. 3,368,396 of Glenn G. Van Burkleo et al, an apparatus is disclosed for controlling the tightness of couplings of well pipe strings. A series of determinations of torque is made for controlling the tightening of the pipe string.
A number of patents have been obtained by Standard Pressed Steel Company, of Jenkintown, Pa., relating to tightening methods and systems utilizing the yield point control concept of the Pauley patent discussed above. These patents include U.S. Pat. No. 3,939,920 of Russell J. Hardiman et al, U.S. Pat. No. 3,974,685 of Richard A. Walker, U.S. Pat. No. 3,974,883 of Jerry A. Sigmund, U.S. Pat. No. 3,982,419 of John T. Boys, and U.S. Pat. No. 4,000,782 of Robert J. Finkelston. U.S. Pat. No. 3,939,920 discloses a system wherein the fastener is brought to its yield point to determine its torque-angular displacement curve, and then after being loosened, is brought back to a preselected portion of the calculated curve.
U.S. Pat. No. 3,974,685 uses a means for determining a false yield, or similar condition of the fastener, so as to determine the specific torque-angular displacement curve for a given fastener and provides control means for then tightening the fastener to a desired load based on that determined curve.
U.S. Pat. No. 3,974,883 discloses a tightening system wherein a theoretical curve is calculated after making a number of gradient determinations with a control means developing a control signal when the theoretical curve and one of the measured signals has a predetermined relation representative of the yield point.
U.S. Pat. No. 4,000,782 discloses means for providing a signal indicating when the wrench and control means are functioning properly and quality control means for continuously checking the different signals.